The present invention relates to a belt tightener of a seat belt for an occupant on a seat in a vehicle, in particular a motor vehicle. The belt tightener has a retracting device, which is actuated by a retracting spring, for automatic shortening of the belt, and an extension lock of the belt, which lock is effective at predetermined parameters, in particular at a predetermined deceleration or acceleration of the vehicle or of its bodywork and/or when a predetermined extension speed of the belt is exceeded. An irreversible tensioning device is preferably provided. On obtaining an accident signal, which can be produced by a sensory mechanism, for example a signal for triggering an airbag, briefly, for example for 10 to 15 ms, the irreversible tensioning device brings about an irreversible tightening of the belt with great force, for example 4000 N.
In a belt tightener of this type currently used as standard in motor vehicles, the retracting device is actuated by a spiral spring which has a structurally predetermined prestress when the belt is pulled in and, when the belt is extended, is increasingly stressed in accordance with its spring characteristic.
The extension lock operates using mechanical catch elements. The latter are controlled, on the one hand, by inertial elements which are shifted from a catch-ineffective position into a catch-effective position if forces acting on the vehicle bodywork bring about a bodywork acceleration or deceleration exceeding a small threshold value. On the other hand, centrifugal elements are deflected from a catch-ineffective position into a catch-effective position if a reel, which is used for accommodating the belt, is rotated at a rotational acceleration exceeding a threshold value or jerkily in the extension direction of the belt. This ensures that the belt is securely locked against (further) extension of the belt in the case of danger-prone driving situations or even accidents.
In view of the fact that the driver and/or—in particular—the front passenger of a vehicle can at least temporarily take up a position outside the normal or desired seat position, irreversible tensioning devices are assigned to the belt tighteners, at least in higher quality vehicles, which devices typically operate pyrotechnically and are triggered if a corresponding sensory mechanism “reports” a collision of the vehicle or triggers an airbag present in the vehicle. These irreversible belt tighteners are used for shortening the seat belt with great force. In this manner, any slack in the belt against the occupant's body and at or on the belt reel is eliminated and also, once a previously triggered airbag is relaxed, ensures optimum safety for the particular occupant in respect of possible secondary collisions. In each case, the occupant is kept as afar away as possible from hard structural parts of the vehicle bodywork.
In order to improve the comfort, it is known, according to German publication DE 39 38 081 A1, to assign an electric motor to the spring provided for actuating the retracting device, in order to adjust the relatively stationary abutment of the retracting spring. In this manner, the belt tension can be changed and the effect can be achieved, in particular, that even with a greatly extended belt, as is necessary if the occupant is of above-average height or plumpness, the belt tension remains low and, accordingly, the wearing comfort is improved. As soon as the belt is withdrawn for winding-up purposes, the relatively stationary abutment is withdrawn into a starting position by the abovementioned motor, so that the belt can be wound up safely.
Similar arrangements are the subject matter of German publications DE 41 12 620 A1, DE 195 01 076 A1 and of international publication WO 01/85495 A2. The last-mentioned publication reveals a belt tightener having a retracting spring, an electric motor which can be activated in a danger situation and a pyrotechnical tightening device.
One object of the invention is to provide a belt tightener which is improved both in respect of comfort and in respect of safety.
This object is achieved according to the invention in the case of a belt tightener of the type mentioned above by including a counterspring having a belt-remote abutment which can be adjusted by a motor arranged parallel to the retracting spring, and a normally open coupling arranged between the motor and the retracting device. The motor can be reversed between two power ranges, and the coupling closes automatically if the motor switches to high power and operates in its running direction provided to give reversible belt tightening.
One general concept of the invention is that of driving the retracting device when the need arises, i.e. in the case of a danger situation determined by sensors, to give reversible tightening of the belt in such a manner that any belt slack which is present is completely withdrawn and the belt is effectively always tightened before an accident can arise from the danger situation. Danger situations can be recognized by sensor, for example, by the fact that the operating state of the vehicle brake and/or accelerations of the vehicle in the longitudinal and transverse direction are detected. A severe brake actuation and/or severe accelerations or decelerations of the vehicle point to hazardous situations.
By means of the reversible belt tightening provided according to the invention, significantly increased safety can therefore be ensured. In particular, the irreversible tensioning device can act more rapidly, so that the occupant is retained at a very early point by the belt during an accident.
On the other hand, the motor, which is provided for the reversible tightening of the belt, provides, by means of its connection or connectability in terms of drive to the belt-remote abutment of the counterspring, the possibility of ensuring particularly great comfort in normal driving situations by the motor adjusting the belt-remote abutment of the counterspring with the effect of reducing the effective tension of the retracting spring, so that the occupant virtually does not notice the belt. In the case of possible movements of the occupant, the belt-remote abutment of the counterspring can temporarily be released or can be adjusted with the effect of increasing the effective pull-back force of the retracting spring, in order to improve the belt retraction which may be necessary.
In a similar manner the tension of the counterspring can also be reduced, and therefore the effective tension of the retracting spring increased, if the belt is released from the belt buckle or remains unused. The belt can thereby be rapidly shortened when not in use and can be kept in the non-use state by means of relatively strong spring force.
The motor provided for adjusting the spring abutment of the counterspring therefore has multiple functions. Firstly, it can improve the wearing comfort of the belt and also facilitate the use of the belt. Secondly, the motor can immediately set a greatly increased belt tension in a danger situation in order to “prepare” the belt system for a possible accident.
According to a preferred embodiment, the motor and/or its driving connection to the belt-remote abutment of the counterspring are designed to be self-locking, so that the set position of the spring abutment is maintained without supply of energy when the motor is at a standstill.
According to a particularly preferred embodiment of the invention, a further coupling is arranged between the motor and the belt-remote abutment of the counterspring, which coupling closes if the motor runs counter to its running direction for the reversible belt tightening.
The coupling, which closes in the case of the reversible belt tightening, is preferably designed as a gradient coupling which is only capable of closing given sufficient differences in speed between the coupling inlet and coupling outlet.
If appropriate, the abovementioned coupling may also be designed as a centrifugal coupling.
In an expedient refinement, a clamping-roller freewheeling device having a braked clamping-roller cage may be provided for this purpose.
Otherwise, with regard to preferred features of the invention reference is made to the claims and the following explanation of the drawing which will be used to describe a particularly preferred embodiment of the invention in greater detail.